.app {
  width: 600px;
  height: 20px;
  background-color: wheat;
  position: relative;
  margin: 0 auto;
}
li {
  list-style: none;
  margin: 0;
}
.app ul {
  padding-left: 0;
}
.app ul li {
  float: left;
}
.app ul li a {
  text-align: center;
  box-sizing: border-box;
  display: inline-block;
  width: 100px;
  height: 20px;
  text-decoration: none;
  border: solid 1px black;
  padding: 0 20px;
  transition: all 1s;
}
.app ul li:nth-of-type(1) a:hover {
  background-color: red;
  color: aqua;
}
.app ul li:nth-of-type(2) a:hover {
  transform: rotate(180deg);
}

.app ul li:nth-of-type(4) a {
  border-radius: 5px;
  animation: spin 1s linear;
  animation-iteration-count: infinite;
}
.app ul li:nth-of-type(4) a:hover {
  animation-play-state: paused;
}

@keyframes spin {
  8% {
    transrorm: rotate(0);
  }
  100% {
    transform: rotate(360deg);
  }
}
